The possibility of being able to capture this data is especially probable since Denver International offers free WiFi and it is an unencrypted network. The probability that a Southwest passenger would login to their account is also quite high since they have an entire terminal to themselves (C concourse). However, this could occur on any unencrypted or encrypted network.
Consider the possibility of a person who is currently (and rightfully) on the Department of Homeland Security's 'No-Fly' list. If this person were able to capture a victim's credentials and create a fake ID, he could pass through TSA security without being stopped.
I don't know how Southwest Airlines let this happen, but sometimes companies have to decide between security and the bottom line. Companies rush to get products out, the engineering dollars are not there to complete the project, so security falls to the back. Usually, security is not thought of as a benefit, until it fails.
I contacted Southwest when the vulnerability was found in early December and they still have not released a patch as of today and they have never contacted me back about the vulnerability. Until the security flaw is fixed, the best solution is to not use the application.
A full list of applications with vulnerabilities can be found here. Additionally, some local NBC and ABC news stations and the Denver Post covered this story."